What Still Has to Be True, No Matter the Method
It would be easy to come away from this companion thinking that RTK, PPK, PPP, and PPP-RTK are four entirely separate worlds, each with its own rules. In one important sense, they are not. Everything this series established before this companion applies to every one of these methods equally, without exception.
A correction method changes only how the raw position is solved. It changes nothing about the reference frame, epoch, geoid model, projection, or verification standards a coordinate must still satisfy afterward, all covered earlier in this series.
The Method Changes One Link, Not the Whole Chain
The second companion in this series followed a coordinate through an entire chain, from a raw geocentric solution through a reference frame, an epoch, a projection, and sometimes a local grid. Every method in this companion changes only the very first link in that chain, how the raw geocentric position gets solved. Nothing downstream of that link cares whether the method was RTK, PPK, PPP, or PPP-RTK. A reference frame still has to be identified. An epoch still has to be recorded. A projection still distorts distance the same way regardless of which method produced the coordinate being projected.
Asking which correction method produced a coordinate is a question about the very first stage of a long chain. Every other stage in that chain proceeds exactly the same way afterward, regardless of the answer.
Trust Still Has to Be Earned the Same Way
The third companion in this series drew a sharp line between precision and accuracy, and between simple redundancy and genuine independent verification. That line does not move for PPK, PPP, or PPP-RTK. A PPP solution that has converged beautifully and repeats consistently has demonstrated precision, exactly the same way a repeatable RTK fix has, and still requires the same kind of independent comparison to demonstrate accuracy. A false or misleading solution is possible with any of these methods, not only with RTK.
A more sophisticated correction method does not exempt a coordinate from the verification standards covered earlier in this series. Precision is still not accuracy, and repeatability is still not correctness, no matter which of the four methods in this companion produced the number.
The One Genuine Difference Worth Remembering
The one place method genuinely does change what gets checked is metadata. A coordinate now needs to record not just its reference frame, epoch, and antenna setup, but which correction method produced it, and for PPK or PPP, which specific precise product was used, since a broadcast-only real-time solution and a final, fully refined post-processed solution from the exact same raw observations can legitimately differ by a small, explainable amount.
A PPP solution processed with final precise products disagrees very slightly from a real-time RTK solution collected at the same location on the same day. Does that disagreement indicate a problem? Not automatically. Different methods, and different product versions within the same method, can produce small, legitimate differences, which is exactly why recording which method and product were used matters as much here as reference frame and epoch always have.
A correction method changes only how the raw position is solved. Reference frame, epoch, geoid model, projection, and verification standards all still apply exactly as this series has already described. The one genuine addition is metadata: recording which method, and which specific product, produced the coordinate.
One short chapter remains, to bring this companion's central lesson to a close.